In view of the fact that recently discovered petroleum oils are increasingly heavy and of high naphthenic acidity, besides being very viscous has created a challenge to be met by the petroleum industry. Petroleum oils having high content in organic acids are strongly corrosive to the equipment used in the extraction, transportation and processing of oil and consequently, any reduction in naphthenic acidity would alleviate corrosion-associated problems.
Those kinds of petroleum oils and their respective liquid fractions having high contents of organic acids are particularly detrimental to the refineries process equipment, especially when those raw materials are used in distillation towers, where high corrosion levels and incrustations have been observed. In Brazil, petroleum oils from the Campos Basin, like Marlin, Albacora e Siri have shown such characteristics and their organic acids are normally naphthenic acids.
U.S. Pat. No. 6,054,042 teaches that naphthenic acidity can be expressed as Total Acid Number (TAN) which means quantity of milligrams of KOH required to neutralize one gram of oil. The analytical method used for the measurements is the D-664 ASTM Method.
Determinations made by infrared spectroscopic analysis allow to estimating the naphthenic acidity contents by measuring the area under the carboxyl characteristic band between 1700 and 1750 cm−1. By combining results from both methods, it is possible to obtain an approximate measure of how much acidity is due to carboxylic acids.
Several approaches to reduce naphthenic acidity in petroleum oils have been adopted in the art.
In order to minimize the problem, one of those is directed to the use of a mix of petroleum oils of different acidity levels.
Another one uses corrosion inhibitor additives to control the acidity. U.S. patents U.S. Pat. No. 5,182,013 and U.S. Pat. No. 4,647,366 teach different types of these inhibitors.
Acidity reduction can yet be obtained by treating oil with basic solutions of NaOH and KOH, as taught in U.S. patent U.S. Pat. No. 4,199,440. However, this method demands the use of strong basic solutions and shows a critical point, which is the formation of hard-to-break stable emulsions. In order to avoid such emulsification problems, an alkaline detergent treatment, based on calcium sulfonate or naphtenate addition is claimed in U.S. Pat. No. 6,054,042.
In U.S. Pat. No. 6,258,258 the use of anhydrous solutions of ammonia is described. In U.S. Pat. No. 6,281,328 polymeric amine solutions, as polyvinyl pyridine are indicated for the same use. U.S. Pat. No. 4,300,995 teaches an oil treatment with a basic solution of quaternary hydroxides, such as tetramethyl ammonium hydroxide, in alcohol or water.
WO 01/79386 teaches the use of a basic solution and metals from group IA, IIA and ammonia hydroxides together with a transfer agent, as the quaternary non-basic salts and polyethers.
U.S. Pat. No. 6,190,541 teaches the use of bases from hydroxides and phosphates with an alcohol.
According to U.S. Pat. No. 6,086,751, acidity may be reduced by thermal treatment. The oil is initially flashed to effect water removal and after that, the effluent is heated to temperatures between 340 and 420° C., pressures below 0.7 MPag and reaction times up to 2 hours.
According to U.S. Pat. No. 5,985,137, naphthenic acidity and sulfur contents of petroleum oils are reduced by reacting with alkaline earth metal oxides, which produce neutralized compounds and alkaline earth metal sulfides. Temperatures must be higher than (or: in excess of) 150° C. to remove carboxylic acids and higher than 200° C. to produce sulfide salts. The applied pressure should be high enough to keep the oil in the liquid state.
Generally, methodologies to reduce the naphthenic acidity make use of thermal treatments that proceed at temperatures around 400° C. and pressures about 1 MPag. However, such methodologies depend on alkaline solution additions to neutralize that acidity. In such cases, the necessity of additional use of surfactants, to control emulsification problems, render the operation more expensive and harder to process. Surfactants are highly expensive chemical products.
Therefore, in spite of the research effort directed to the problem of minimizing naphthenic acidity in petroleum oils, the technique still needs a process directed to reducing the level of naphthenic acids to acceptable grounds, such a process, based on a thermal treatment in the presence of coked (spent) Fluid Catalytic Cracking (FCC) catalysts being described and claimed in the present invention.